A Little Young
by Maethorelen
Summary: When a vacation to New York goes awry, Phineas, Ferb, and Isabella decide to take part in the battle to save mankind. "Aren't they a little young to help save the world?" "Yes, yes they are." One-shot.


**Hey everybody! This charming little one-shot was born out of boredom on a 5-hour flight back home from vacation. I had watched the Avengers (again) while on the trip, and I also went to Epcot and did _Agent P's World Showcase Adventure_, which kind of inspired me to write this. Warning: this may be a bit silly in some parts due to the fact that it was born out of boredom, and even I don't know where my brain wanders when I'm bored.**

**This mainly focuses on Phineas, Ferb, and Isabella. There is a little of Perry and Doofenshmirtz, but not too much. In this story, Candace has no clue what those three are up to, so no busting (my apologies). Anyways, hope you enjoy!**

**Disclaimer: I own nothing. _Phineas and Ferb_ and their characters are owned by Disney, and _The Avengers_ are owned by Marvel.**

A Little Young

The Flynn-Fletcher family, along with Isabella, drove down the winding road, passing a sign reading, "Welcome to New York". Phineas and Ferb had also invited Baljeet and Buford, but Baljeet had a mathematics camp to attend and Buford didn't want to miss the annual Bully Games.

"Ferb, Isabella, we're almost there!" Phineas exclaimed excitedly from the back seat. "New York, here we come!"

"I can't wait to visit Stark Tower," Isabella stated. " I heard that it was powered by its own arc reactor, making it capable of sustaining itself for at least a year."

"Hey Ferb," Phineas called, "do you think we'll be able to meet Tony Stark? I mean, I know he's busy being Iron Man and all, but still, a guy can hope."

"Well, unless there is some world-destroying crisis, I'm pretty sure he'll be available," Ferb replied. "That is, of course, if he isn't throwing any high-class parties."

Isabella sighed. "Ah, the life of a genius billionaire superhero."

"Too bad we had to leave Perry at home," Phineas stated. "He would have really enjoyed this."

"Alright, everyone, we're here!" Lawrence announced from the driver's seat, parking their red minivan in front of a tall red brick hotel in Manhattan.

"Ferb, Isabella, check it out!" Phineas exclaimed, examining the map. "Stark Tower is only a few miles away!"

"Ugh, that ugly thing?" Candace scoffed. "Please, why would anyone want to visit that weird excuse for a skyscraper?"

"Actually, it's the first of its kind," Isabella corrected. "It combines very modern architecture with high-tech machines to make for one very impressive building."

Candace rolled her eyes. "Pfft, whatever."

The six quickly checked into the hotel and found their rooms. "Okay you four, here are your bus passes." Linda handed a card each to Phineas, Ferb, Isabella, and Candace. "Your dad and I are going to head over to the antique fair in New York City. Candace, while we're gone, you're in charge." Lawrence and Linda strode out of the hotel and into the car, driving out of the parking lot.

"Yes!" Candace cheered. "You hear that?" she taunted the three youngest. "I'm in charge! So that means no building any crazy, bustable contraptions. For once, I want one of our trips to go as planned, with absolutely nothing strange or out of this world happening."

"Oh, don't worry, Candace," Phineas reassured her. "The only thing we plan on doing is seeing some Stark technology."

"Alright, fine, you three go visit that weird building while I do some shopping." Candace grabbed her purse and walked out of the door. "I promised Stacy I'd get her a nice purse."

Phineas watched his sister exit the hotel before turning to Ferb and Isabella. "Come on, gang, let's go!" The three raced out to the bus stop, jumping on the soonest bus. Within minutes, they arrived on the street of Stark Tower, all three of then nearly shaking with excitement.

"I wonder if I can earn my 'Using Futuristic Technology' patch," Isabella pondered. Phineas opened his mouth to answer, but he was interrupted by the sound of a rocket blasting through the sky. The threesome looked up to see a huge, shining red missile soaring towards the falling shape of a man. As the rocket neared the man, it slowly began to break apart, latching onto the man's spread-eagled form and constructing the familiar hot rod red and gold armor of the Iron Man.

"Whoa, that was awesome!" Phineas exclaimed. His triangular face suddenly clouded with concern. "Uh, Ferb, you said that Iron Man would only be out if there was a world-destroying crisis, right?" Ferb silently nodded his head. Phineas's eyes went wide. "Then that means..."

Ferb finished the sentence for his brother. "...we're in the middle of a world-destroying crisis." The three gazed upward at Stark Tower to see a brilliant jet of blue light blast a black hole in the sky, thousands of gray alien creatures beginning to pour out.

"What should we do, Phineas?" Isabella asked worriedly.  
Phineas brought his hand to his lips (since he doesn't have a chin) in thought. After a few moments, his face brightened. "Hey Ferb, did you bring the portable Superpower Packs?" Ferb nodded, pulling out three compact cubes.

Isabella cocked her head in confusion. "When did you two build Superpower Packs?"

"We created them last week as a bit of a side project," Phineas explained. "I wanted to show Tony Stark the technology, but I guess we'll have to use them in combat instead. That wasn't my original intention when I made the plans for these, but I think it should work." He handed Isabella one of the cubes, taking another one for himself. All three of them grabbed the open tabs on the cubes. Phineas gazed at his two friends. "Alright gang, let's suit up!"

~o*o*o*o~

Meanwhile, back in Danville, Perry the Platypus was sitting in the Garcia-Shapiro house, where he was staying until the Flynn-Fletchers returned home. Everything was relatively peaceful around the neighborhood, no signs of Doofenshmirtz's schemes to be found. Suddenly, the secret agent watch Perry wore beneath his fur began to beep loudly, displaying the "red alert" signal. Hurriedly, Perry donned his fedora and raced across the street, swiftly sliding down the tube to his secret hideout. Klaxons were blaring loudly in the room, and red lights were flashing along the walls. Perry leapt into his chair, turning on the monitor to find an extremely distressed Major Monogram.

"Agent P," Monogram addressed. "It pains me to say this, but we are in the middle of a world-threatening crisis! Unfortunately, all of our other agents are out of the country on other missions, so we will need to send you into the field instead. All of Dr. Doofenshmirtz's activities must be put to the side for now. The O.W.C.A. has teamed up with the Strategic Homeland Intervention Enforcement and Logistics Division, or S.H.I.E.L.D.. Here is Agent Maria Hill from S.H.I.E.L.D. to brief you on the situation."

The screen of the monitor split in two, the right half of the screen now occupied by a young woman in a dark blue uniform, her brown bangs falling slightly in her face. "Agent P," she began. "I..." Agent Hill trailed off as she studied the agent she was to be briefing. She turned away from the screen, addressing someone behind her. "Director Fury, sir, you didn't inform me that I was dealing with a platypus agent."

"Agent Hill," a deep voice from off-screen replied. "This branch of government security is run by a bunch of crazies. All their agents are animals of some kind."

"Hey!" Major Monogram protested. "Having animal agents reduces the cost for travel and, uh...makes it easier for them to disguise themselves as common household pets."

Agent Hill just rolled her eyes. During her time working for S.H.I.E.L.D., she had seen stranger. "Anyways, continuing with the mission briefing," she stated. A picture appeared on the top right corner of the screen. It depicted a dark-haired man dressed in dark green and black leather, a mischievous smile on his face. "This is Loki of Asgard," Agent Hill informed him. "He intends to unleash an army upon the Earth and rule us as our king. Loki has escaped our headquarters less than an hour ago and has made his way to Stark Tower. We need you to help apprehend him and stop his army. A team of heroes is already en route, but they could use all the help the can get. Good luck, Agent P."

Agent Hill's side of the screen blinked out, leaving only Major Monogram with Perry. "Well, you heard her, Agent P," Monogram stated. "Stop this Loki of Asgard before it's too late. Monogram out." Perry gave the Major a quick salute before taking off in his platypus-sized rocket car to New York.

Major Monogram stared at the empty orange chair in front of him. "S.H.I.E.L.D.," he wondered aloud. "Carl, why can't we have a cool acronym like that?"

"Sorry, sir," the red-headed intern replied. "We did our best to come up with a good acronym. O.W.C.A. was the best one we had."  
Monogram huffed frustratedly. "Oh, I suppose."

~o*o*o*o~

Dr. Doofenshmirtz stood in his Evil Incorporated building, staring at the door. "Any second now, Perry the Platypus will bust in, leaving a rather large platypus-sized hole in my door, and step onto that tile square, where I will trap him before going about our usual routine," Doofenshmirtz muttered to himself. "You know, I tell him my evil scheme, he escapes, he somehow thwarts - hey!"

Dr. Doofenshmirtz quickly picked up the piece of paper that had been slipped beneath his door. "Dear Dr. Heinz Doofenshmirtz," he read. "Due to a recent world-ending crisis, your interactions with Agent P have been put on hold... On hold?" Doofenshmirtz quickly scanned through the rest of the letter. "Who does this 'Loki of Asgard' think he is, taking away my nemesis time! Oh, and he's saying that he's some god of mischief; well, I'll show him mischief! With a side of evil! Oh, and maybe some fries too. Ah, whatever. Now, if I could only find out where he is..."

~o*o*o*o~

Phineas gazed around at his two companions' supersuits, both custom-tailored for each of them. Isabella's consisted of a bright purple short-sleeved tee and dark violet pants, both made of flexible cloth resilient to fire, water, and staining. A powerful jetpack was strapped to her back, allowing her to fly, and a white sash was slung across her shoulder, engineered to lengthen and shorten to Isabella's needs. Ferb had donned a pair of blue-rimmed goggles, a full tank of water strapped to his back which connected to the two powerful hoses he held in his hands. He also wore a navy blue chestpiece, created from a lightweight alloy of metals. Phineas's suit was bright orange, made from the same material as Isabella's. A rocket booster had been fitted to each of his shoes for super-speed, and a small toy pellet gun was in a holster at his side. "Awesome!" he cheered, ecstatic that the suits deployed perfectly. "Hey Isabella, are you ready to earn your 'Assisting a Superhero' patch?"

"You betcha!" Isabella replied. "I might also be able to earn my 'Stopping a World-Ending Crisis' patch too."

A smile broke out on Phineas's face. "Then let's get started! Team Danville, move out!"

The three raced out onto the battlefield, knocking aliens down here and there. Isabella took to the skies with her jetpack, using her sash to yank their hovercrafts off course and into buildings. Phineas and Ferb fought side by side on the ground, alternately spraying the aliens with water and hitting them on the head with pellets. The battle continued on like that for several minutes, until a jet nearly hit them as it collided with the ground.

~o*o*o*o~

Captain America climbed of the wreck of the Quinjet, closely followed by Black Widow and Hawkeye. The three surveyed the damage the Chitauri had done to the city. Cars had been flipped over, buildings were blackened and damaged, and civilians were running around in a screaming panic. Well, most of them were. Three children standing off to the side near the Quinjet caught the attention of the Captain. For one, they didn't seem to be fazed at all by the battle around them, as if they had dealt with aliens before. They also weren't wearing normal civilian clothes. All three had some sort of gadget strapped to them, almost like a young team of superheroes.

"Phineas, Ferb, are you guys alright?" the young girl asked urgently. She had long dark hair adorned with a bright purple bow, with what seemed to be a jetpack on her back.

The young boy with the triangular head nodded. "I'm fine Isabella," he answered. "What about you, Ferb?" The green-haired boy gave the two others a silent thumbs up, dusting off the chestplate he was wearing.

"Excuse me," Steve interrupted politely. "You three should get to somewhere safe now. A big battle is about to happen here. It's too dangerous for three kids to be out on the field."

"But sir," the young girl protested. "We want to help!"

"Yeah," the red-haired boy agreed. The other boy nodded, not saying a word.

Steve opened his mouth to reply, but Natasha cut him off. "Captain, I was watching them while we were in the air. They put up a really good fight against the Chitauri." She turned to face the three kids. "They have a lot of potential."

"Hey you three!" Tony's voice suddenly sounded into the Avengers' earpieces. "What took you so long?" The Iron Man zoomed above the wreck of the Quinjet, observing the situation. "Who's that you're talking to?"

"They're a few kids we met," Steve answered. He let out a deep breath, unsure if what he was about to say was the right choice. "They're here to help us."

Tony quirked his head in confusion. "Aren't they a little young to help save the world?"

Natasha sighed. "Yes, yes they are."

"Well, it's fine with me," Tony replied. "We could use all the help we can get."

Clint turned to the three kids. "Looks like you guys are in."

"Awesome!" the triangular-headed one cheered. "I'm Phineas, and this is my brother Ferb." He gestured to the quiet boy. "And this is our friend Isabella."

"Nice to meet you," the young girl greeted sweetly.

The Black Widow nodded. "I'm Natasha Romanoff, and this is Captain Steve Rogers and Clint Barton. And I assume you've heard of Tony Stark?" All three nodded, smiles present on their faces. Natasha could understand the feeling; nothing gave her as much excitement and adrenaline as missions. She handed each kid a comlink. "Use these to keep in touch with the others."

Phineas put his in his ear. "Testing, one, two."

"I copy, Phineas," Isabella answered. "Now let's do this!"

~o*o*o*o~

Perry soared through the sky on his rocket car, headed straight for Stark Tower. Suddenly a transmission came in from O.W.C.A. headquarters. The face of Major Monogram appeared on the screen, his expression worried. "Agent P," he addressed. "It seems that Dr. Doofenshmirtz has attempted to go after Loki. You need to reroute him and get him out of Manhatten as quickly as possible." Perry gave the Major a quick salute before whirling his car around, only to collide straight into Dr. Doofenshmirtz's hovercraft.

"Oh, Perry the platypus, how good to see you again," Doofenshmirtz greeted. "Do you happen to know where this..." He quickly referred to his paper. "...this 'Loki of Agard' is?"

Perry quickly shook his head before leaping over the doctor's head to reach the controls of the hovercraft. "Hey, Perry the platypus, what're you doing?" Doofenshmirtz asked as Perry swung the craft around. "We should be heading into the city, not out of it!"

The platypus ignored the doctor, navigating his way through the streets. The hovercraft came to a screeching halt, however, when Perry spotted a few familiar faces in the chaos below. He let out a chatter of surprise,wondering why in the world Phineas, Ferb, and Isabella were out in the field. This pause was just long enough for one of the Chitauri to score a direct hit to one of the main thrusters, causing the craft to wobble, one side in flames.

Doofenshmirtz screamed, terrified of the attackers. "You know what, Perry the platypus, I've changed my mind. GET US OUT OF HERE!"

Perry nodded, swerving to avoid the swarms of Chitauri. Doofenshmirtz yelled in terror, clinging on to the platypus for dear life. The hovercraft was slowly losing power, plummeting to the earth. "Perry the platypus, we're going to crash!" Doofenshmirtz shouted. Perry quickly pulled out his jetpack and grabbed the doctor, soaring up into the sky just as the hovercraft crashed into the street. "Oh, Perry the platypus, you saved us!" Doofenshmirtz exclaimed as they flew above the skyscrapers and out of the city. "Thank you Perry the platypus!"

Perry just smiled as he began the long journey back to Danville.

~o*o*o*o~

"Hey Phineas," Isabella asked. "What'cha doing?"

"Right now, I'm taking on a squadron with Clint," he answered. "You?"

"Bringing down some Chitauri with Iron Man," she answered. The three of them had been quickly briefed on the situation before heading out to battle and now had a slight grasp of what they were dealing with.

"You know, that girl packs a wallop," Tony commented, flying up to Isabella.

The young girl blushed. "Gee, thanks!"

"Hey, Stark," Clint called from the ground. "Thor's arrived."

Tony cocked his head. "Really now?"

"Yeah," Phineas confirmed. "He's taking down a couple with Ferb."

"Great," Tony replied. "Has Banner come yet?"

"Banner?" Steve asked. The captain gazed at his surroundings. There was Natasha, firing one of the Chitauri's own weapons back at them from beside him. Clint and Phineas were down the street, taking out the Chitauri with arrows and those annoying pellets from Phineas's weapon. Ferb and Thor were around the corner, battling the oncoming aliens with hammer and water. But there was no sign of the doctor, nor his big green counterpart. "No, he's not here."

Tony sighed. "Well, keep me posted."

Steve nodded, dodging a few enemy blasts. The super soldier darted across the field towards Phineas just as Clint sprinted over to Natasha. "Hey Captain," the young boy greeted cheerfully, as if they were just two friends getting lunch.

"Have you and your friends dealt with aliens before?" Steve asked, puzzled by the kids' attitudes. They didn't seem terrified at all, as if this was an everyday occurrence.

"Well, yeah," Phineas answered. "We had to help our alien friend Meap defeat an intergalactic villain named Mitch twice. Then we helped a couple of aliens find their key by following a bunch of crop circles, but that doesn't really have anything to do with the situation." He paused for a moment, speeding off towards Clint and Natasha to fire some pellets at some of the Chitauri that had managed to dodge their bullets and arrows. Steve followed, leaping over a car wreck and ducking behind a fallen truck. "But we've really never done anything like this before!" Phineas continued, shouting over the noise of battle. "It's actually kind of fun!"

Steve shook his head, a hint of a smile on his face. The kid's optimism was quite comforting in a time like this. Together, he, Clint, Natasha and Phineas continued to battle the Chitauri. They were quickly joined by Thor and Ferb, and the legion of Chitauri soon fell. Suddenly, the soft hum of a motorbike engine could be heard as Dr. Banner rolled up to them, studying the surrounding carnage. "Well, this all looks horrible," he commented dryly.

Natasha smiled grimly. "I've seen worse."

The doctor suddenly looked very apologetic. "I'm sorry you had to see that."

"No, it's alright," Natasha replied. "We could use a little worse."

"Stark, we got him," Steve called into the comlink.

"Banner?" Tony asked.

Steve nodded. "Yes, just like you said."

"So that's Dr. Banner," Phineas stated.

"Yep kid, that's the doc," Tony replied. "Tell him to suit up. We're bringing the party to you."

The rod red and gold suit of the Iron Man rocketed around the corner, closely followed by a familiar purple suit.

"Isabella?" Phineas asked incredulously.

"This was all his idea, Phineas!" Isabella shouted back. Suddenly, a loud roar rattled the street as a humongous metal beast rounded the corner, fiery red eyes aglow as it chased the two flying superheroes down the street.

Natasha shook her head. "I don't see how that's a party."

"I also fail to see the 'party' element," Phineas added.

Ignoring the two, Steve stepped towards Bruce. "Doctor, now might be a good time to get angry."

"That's my secret, Cap," Bruce replied, beginning to step towards the Leviathan. "I'm always angry." The doctor tensed his muscles, his body slowly becoming green and enlarging in size. His shirt fell away like paper as the Hulk was released, smashing his huge green fist into the head of the Leviathan.

Phineas, Ferb, and Isabella all gaped in awe as the Leviathan's head was slammed into the ground, its long metal body flipping up and towering over them. "Hold on!" Tony yelled, hovering above them. He lifted the gauntlet of his suit, firing a missile directly into the beast. The Leviathan engulfed in a brilliant explosion, causing all the Avengers to duck for cover. Parts of the beast's great metal body tumbled off the edge of the highway, and several Chitauri roared at the destruction. The Avengers, including Phineas, Ferb, and Isabella, stood in a circle around the wreck, staring defiantly up at the Chitauri and prepping their weapons for battle.

Meanwhile, on the bridge of the Helicarrier, Director Nick Fury and his second-in-command Maria Hill were watching the battle footage of New York. "Sir, there seems to be three children fighting beside the Avengers," Agent Hill remarked. "Should I tell them to pull them out?"

"No," Fury replied, his eyes not leaving the screen.

Agent Hill looked at the Director in confusion. "But why, sir?"

The Director looked up from the screen, gazing through the windows on the bridge. "Because in times like this, we could use all the help we can get, no matter how young."

**So, I hope you guys enjoyed this. It was really fun to write. Oh, and please review! (Seriously, does that review box keep getting more obnoxious or what?)**


End file.
